Optical articles that provide good imaging qualities while reducing the transmission of incident light into the eye are needed for a variety of applications, such as sunglasses, vision correcting ophthalmic lenses, plano lenses and fashion lenses, e.g., non-prescription and prescription lenses, sport masks, face shields, goggles, visors camera lenses, windows, automotive windshields and aircraft and automotive transparencies, e.g., T-roofs, sidelights and backlights.
In response to certain wavelengths of electromagnetic radiation (or actinic radiation), photochromic materials undergo a transformation from one form or state to another form, with each form having a characteristic or distinguishable absorption spectrum associated therewith. Typically, upon exposure to actinic radiation, many photochromic materials are transformed from a closed-form, which corresponds to an unactivated (or bleached, e.g., substantially colorless) state of the photochromic material, to an open-form, which corresponds to an activated (or colored) state of the photochromic material. In the absence of exposure to actinic radiation, such photochromic materials are reversibly transformed from the activated (or colored) state, back to the unactivated (or bleached) state.
Photochromic plastic articles used for optical applications have been the subject of considerable attention. In particular, photochromic ophthalmic plastic lenses have been of interest because of the advantages associated with reduced weight that they can provide compared to glass lenses. Photochromic optical articles typically display colorless (e.g., clear) and colored states that correspond to the colorless and colored states of the photochromic materials contained therein. Photochromic compounds can be incorporated into optical articles, by methods including, imbibing a photochromic compound directly into an optical substrate, or by forming a photochromic coating layer over an optical substrate, which contains a photochromic compound.
When a photochromic coating composition is applied over a surface of an optical substrate, insufficient wetting of the surface by the photochromic coating composition can occur. Insufficient wetting of the surface by the photochromic coating composition can require the application of additional photochromic coating composition over the surface to ensure the formation of a uniform photochromic coating layer thereover. In some application methods, such as spin coating methods, some of the excess or additionally applied photochromic coating composition is ejected off of the edges of the rotating optical substrate. While the ejected photochromic coating composition can be collected and recycled, due to contamination concerns, the ejected photochromic coating composition is often disposed of as waste or a waste stream.
Photochromic compounds can be expensive. As such, it would be desirable to develop new methods of forming photochromic coating layers on optical substrates that require the application of a minimum or reduced amount of photochromic coating composition thereover. In addition, it would be desirable that such newly developed methods minimize or reduce the amount of photochromic coating composition waste that is formed during such coating processes.